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Attitude metrology (roll, pitch, and yaw) plays an important role in many different fields. Roll angle is considered the most difficult measurement quantity in angular displacements compared to pitch and yaw angles because the rotation axis of the roll angle is parallel to the probe beam. In this work, a sensitivity enhanced roll-angle sensor is presented. The principle is based on the polarization change of a sensing unit (quarter-waveplate). The polarization model is analyzed by Mueller matrix formalism. The Stokes parameters are detected by a Stokes polarimeter. The novel coaxial design improves the sensitivity and reduce the complexity of optical system alignment by means of a fixed quarter-waveplate. The proposed sensor provides a simple setup to measure roll angles with a high sensitivity of 0.006∘ and a long unambiguous measurement range of 180∘.